Answer: b
Explanation: A megaprimer method is an approach of carrying out mutagenesis by using PCR. It is a two stage approach and uses three oligonucleotide primers.

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2. Choose the correct statement.
a) There are two flanking primers and they are having mutations
b) There is one primer which anneals the target sequence and is having mutation
c) Either of the flanking primers or the primer is annealing to the target sequence is having mutation
d) One of the flanking primer and the primer annealing to the target sequence is having mutationView Answer

Answer: b
Explanation: In the megaprimer approach three primers are used. There are two primers which flank the target sequence and a third primer anneal to the target sequence. The mutation is there in the third primer.

3. PCR using the mutagenic primer and one of the flanking primers is used to carry out amplification and generates a product corresponding to the part of the gene. It is called as megaprimer.
a) True
b) FalseView Answer

Answer: a
Explanation: Megaprimer is produced when amplification is carried out by using mutagenic primer and one of the flanking primers. It corresponds to the part of the gene.

4. Sometimes mutagenesis is carried out with the help of primers. Choose the correct statement with respect to it.
a) Double stranded circular molecule is used as a template
b) Mutation is introduced into one of flanking primers
c) Single stranded circular molecule is used as a template
d) After amplification, mutation is introduced into one strandView Answer

Answer: a
Explanation: Double stranded circular molecules are used as a template. Mutation is introduced into both of the primers and then amplification is carried out. After amplification is carried out, mutation can be introduced either in one strand or both the strands.

5. If PCR is used to introduce random mutations rather than specific mutations, it is called as ___________
a) mutagenic PCR
b) error-prone PCR
c) random PCR
d) general PCRView Answer

Answer: b
Explanation: At times, PCR is used to introduce random mutations, rather than specific mutations and this type of PCR is called as error-prone PCR. There can be either one or many mutations.

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6. For the selection of the molecules having mutated sequence, which of the statement is true?
a) It is suitable for methods which are PCR based
b) It is suitable for methods which are not PCR based
c) It is suitable for both PCR and not PCR based
d) Selection of molecules with the mutant sequence is not possibleView Answer

Answer: b
Explanation: Selection is done either of molecules having a mutant sequence or degradation of wild type molecules is carried out. For selection of molecules having a mutant sequence, it can be used for methods which are not PCR based.

7. Choose the incorrect statement for the methodology of selection of molecules with mutant sequences.
a) A vector is used which is having antibiotic resistance gene
b) Apart from antibiotic resistance gene, a second antibiotic resistance gene is also present
c) There are two mutagenic primers which are used
d) The second strand synthesis is carried out by only one primerView Answer

Answer: d
Explanation: A vector is used which is having conventional antibiotic resistance and along with a second antibiotic resistance gene. The second gene is inactivated because of point mutation. Also, there are two mutagenic primers used. The first primer is used for directing the incorporation of mutation. The second primer makes the inactive gene inactive. Both the primers are used for second strand synthesis.

8. Once second strand synthesis is carried out, it is introduced into the host. Host is having which mutation?
a) mutS mutation
b) mutD mutation
c) mutE mutation
d) mutG mutationView Answer

Answer: a
Explanation: The host is having a mutS mutation. And because of this mutation, no mismatch repair takes place.

Answer: b
Explanation: Replication can be either by first strand or second strand. First strand replication leads to generation of wild type molecules and the antibiotic resistance is inactive. If the replication is carried out by second strand, mutated sequence is formed and the antibiotic resistance gene becomes active.

Answer: d
Explanation: In a phosphothiorate nucleotide, oxygen atom is replaced by a sulphur atom. Because of this replacement the DNA molecule becomes resistant to attack by nucleases.

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11. What is the function of ung gene?
a) It is responsible for deamination of cytosine
b) It is responsible for deamination of uracil
c) It is responsible for removal of uracil
d) It is responsible for removal of cytosineView Answer

Answer: c
Explanation: Ung gene is responsible for the removal of uracil. It does it by the enzyme Uracil-N-glycosylase and apyrimidinic site is created.